Magnetic head and system having offset arrays

ABSTRACT

A computer program product for orienting a head includes a computer readable storage medium having program instructions embodied therewith. The program instructions are readable and/or executable by a controller to cause the controller to: determine a desired pitch for transducers for reading and/or writing to a magnetic tape; and cause a mechanism to orient a head to achieve the desired pitch. The array of a first of the modules is offset from the array of a second of the modules in a first direction parallel to the axis of the array of the second module such that the transducers of the first module are about aligned with the transducers of the second module in the intended direction of tape travel thereacross when the axes are oriented at an angle greater than 0.2° relative to a line oriented perpendicular to the intended direction of tape travel.

BACKGROUND

The present invention relates to data storage systems, and moreparticularly, this invention relates to a magnetic head and systemimplementing the same, where the head has offset arrays.

In magnetic storage systems, data is read from and written onto magneticrecording media utilizing magnetic transducers. Data is written on themagnetic recording media by moving a magnetic recording transducer to aposition over the media where the data is to be stored. The magneticrecording transducer then generates a magnetic field, which encodes thedata into the magnetic media. Data is read from the media by similarlypositioning the magnetic read transducer and then sensing the magneticfield of the magnetic media. Read and write operations may beindependently synchronized with the movement of the media to ensure thatthe data can be read from and written to the desired location on themedia.

An important and continuing goal in the data storage industry is that ofincreasing the density of data stored on a medium. For tape storagesystems, that goal has led to increasing the track and linear bitdensity on recording tape, and decreasing the thickness of the magnetictape medium. However, the development of small footprint, higherperformance tape drive systems has created various problems in thedesign of a tape head assembly for use in such systems.

In a tape drive system, magnetic tape is moved over the surface of thetape head at high speed. Usually the tape head is designed to minimizethe spacing between the head and the tape. The spacing between themagnetic head and the magnetic tape is crucial so that the recordinggaps of the transducers, which are the source of the magnetic recordingflux, are in near contact with the tape to effect writing sharptransitions, and so that the read element is in near contact with thetape to provide effective coupling of the magnetic field from the tapeto the read element.

The quantity of data stored on a magnetic tape may be increased byincreasing the number of data tracks across the tape. More tracks aremade possible by reducing feature sizes of the readers and writers, suchas by using thin-film fabrication techniques and MR sensors. However,for various reasons, the feature sizes of readers and writers cannot bearbitrarily reduced, and so factors such as lateral tape motiontransients and tape lateral expansion and contraction (e.g.,perpendicular to the direction of tape travel) must be balanced withreader/writer sizes that provide acceptable written tracks and readbacksignals. One issue limiting areal density is misregistration caused bytape lateral expansion and contraction. Tape width can vary by up toabout 0.1% due to expansion and contraction caused by changes inhumidity, tape tension, temperature, aging etc. This is often referredto as tape dimensional stability (TDS).

If the tape is written in one environment and then read back in another,the TDS may prevent the spacing of the tracks on the tape from preciselymatching the spacing of the reading elements during readback. In currentproducts, the change in track spacing due to TDS is small compared tothe size of the written tracks and is part of the tracking budget thatis considered when designing a product. As the tape capacity increasesover time, tracks are becoming smaller and TDS is becoming anincreasingly larger portion of the tracking budget and this is alimiting factor for growing areal density.

SUMMARY

In one general embodiment, a computer program product for orienting ahead includes a computer readable storage medium having programinstructions embodied therewith. The program instructions are readableand/or executable by a controller to cause the controller to: determine,by the controller, a desired pitch for transducers for reading and/orwriting to a magnetic tape; and cause, by the controller, a mechanism toorient a head to achieve the desired pitch, the head having at least twoopposing modules generally aligned with each other in an intendeddirection of tape travel thereacross, positions of the two modules beingfixed relative to each other, each module having an array of thetransducers. An axis of each array is defined between opposite endsthereof. The array of a first of the modules is offset from the array ofa second of the modules in a first direction parallel to the axis of thearray of the second module such that the transducers of the first moduleare about aligned with the transducers of the second module in theintended direction of tape travel thereacross when the axes are orientedat an angle greater than 0.2° relative to a line oriented perpendicularto the intended direction of tape travel.

This embodiment may be implemented in a magnetic data storage systemsuch as a tape drive system, which may include a magnetic head, a drivemechanism for passing a magnetic medium (e.g., recording tape) over themagnetic head, and a controller electrically coupled to the magnetichead.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a simplified tape drive systemaccording to one embodiment.

FIG. 1B is a schematic diagram of a tape cartridge according to oneembodiment.

FIG. 2 illustrates a side view of a flat-lapped, bi-directional,two-module magnetic tape head according to one embodiment.

FIG. 2A is a tape bearing surface view taken from Line 2A of FIG. 2.

FIG. 2B is a detailed view taken from Circle 2B of FIG. 2A.

FIG. 2C is a detailed view of a partial tape bearing surface of a pairof modules.

FIG. 3 is a partial tape bearing surface view of a magnetic head havinga write-read-write configuration.

FIG. 4 is a partial tape bearing surface view of a magnetic head havinga read-write-read configuration.

FIG. 5 is a side view of a magnetic tape head with three modulesaccording to one embodiment where the modules all generally lie alongabout parallel planes.

FIG. 6 is a side view of a magnetic tape head with three modules in atangent (angled) configuration.

FIG. 7 is a side view of a magnetic tape head with three modules in anoverwrap configuration.

FIGS. 8A-8C are partial top-down views of one module of a magnetic tapehead according to one embodiment.

FIGS. 9A-9C are partial top-down views of one module of a magnetic tapehead according to one embodiment.

FIG. 10A is a partial top-down view of an apparatus with two modulesaccording to one embodiment.

FIG. 10B is a diagram of the system having the apparatus of FIG. 10A.

FIG. 10C is a partial top-down view of an apparatus with two modulesaccording to one embodiment.

FIG. 10D is a partial top-down view of a system with multiple sets ofmodules according to one embodiment.

FIG. 11 is a flow chart of a method according to one embodiment.

FIG. 12 is a partial top-down view of a magnetic head with three modulesaccording to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof.

In one general embodiment, an apparatus includes at least two modules,each of the modules having an array of transducers, wherein the at leasttwo modules are fixed relative to each other, wherein an axis of eacharray is defined between opposite ends thereof, wherein the axes of thearrays are oriented about parallel to each other, wherein the array of afirst of the modules is offset from the array of a second of the modulesin a first direction parallel to the axis of the array of the secondmodule such that the transducers of the first module are about alignedwith the transducers of the second module in an intended direction oftape travel thereacross when the axes are oriented at an angle greaterthan 0.2° relative to a line oriented perpendicular to the intendeddirection of tape travel thereacross; and a mechanism for orienting themodules to control a transducer pitch presented to a tape.

In another general embodiment, an apparatus includes at least twomodules, each of the modules having an array of transducers, a drivemechanism for passing a magnetic medium over the modules; a mechanismfor orienting the modules to control a transducer pitch presented to atape; and a controller configured to control the mechanism for orientingthe modules based on a state of expansion of the tape, wherein the atleast two modules are fixed relative to each other, wherein an axis ofeach array is defined between opposite ends thereof, wherein the axes ofthe arrays are oriented about parallel to each other, wherein the axesare oriented at an angle greater than 0.2° relative to a line orientedperpendicular to an intended direction of tape travel thereacross,wherein the array of a first of the modules is offset from the array ofa second of the modules in a first direction parallel to the axis of thearray of the second module such that the transducers of the first moduleare about aligned with the transducers of the second module in theintended direction of tape travel thereacross.

In yet another general embodiment, a computer program product fororienting a head includes a computer readable storage medium havingprogram code embodied therewith. The program code is readable/executableby a controller to: determine, by the controller, a desired pitch fortransducers for reading and/or writing to a magnetic tape; and cause amechanism to orient a head to achieve the desired pitch, the head havingat least two opposing modules generally aligned with each other in anintended direction of tape travel thereacross, positions of the twomodules being fixed relative to each other, each module having an arrayof the transducers. An axis of each array is defined between oppositeends thereof. The array of a first of the modules is offset from thearray of a second of the modules in a first direction parallel to theaxis of the array of the second module such that the transducers of thefirst module are about aligned with the transducers of the second modulein the intended direction of tape travel thereacross when the axes areoriented at an angle greater than 0.2° relative to a line orientedperpendicular to the intended direction of tape travel.

FIG. 1A illustrates a simplified tape drive 100 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 1A, it should be noted that the embodiments described herein may beimplemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 areprovided to support a tape 122. One or more of the reels may form partof a removable cartridge and are not necessarily part of the system 100.The tape drive, such as that illustrated in FIG. 1A, may further includedrive motor(s) to drive the tape supply cartridge 120 and the take-upreel 121 to move the tape 122 over a tape head 126 of any type. Suchhead may include an array of readers, writers, or both.

Guides 125 guide the tape 122 across the tape head 126. Such tape head126 is in turn coupled to a controller 128 via a cable 130. Thecontroller 128, may be or include a processor and/or any logic forcontrolling any subsystem of the drive 100. For example, the controller128 typically controls head functions such as servo following, datawriting, data reading, etc. The controller 128 may operate under logicknown in the art, as well as any logic disclosed herein. The controller128 may be coupled to a memory 136 of any known type, which may storeinstructions executable by the controller 128. Moreover, the controller128 may be configured and/or programmable to perform or control some orall of the methodology presented herein. Thus, the controller may beconsidered configured to perform various operations by way of logicprogrammed into a chip; software, firmware, or other instructions beingavailable to a processor; etc. and combinations thereof.

The cable 130 may include read/write circuits to transmit data to thehead 126 to be recorded on the tape 122 and to receive data read by thehead 126 from the tape 122. An actuator 132 controls position of thehead 126 relative to the tape 122.

An interface 134 may also be provided for communication between the tapedrive 100 and a host (integral or external) to send and receive the dataand for controlling the operation of the tape drive 100 andcommunicating the status of the tape drive 100 to the host, all as willbe understood by those of skill in the art.

FIG. 1B illustrates an exemplary tape cartridge 150 according to oneembodiment. Such tape cartridge 150 may be used with a system such asthat shown in FIG. 1A. As shown, the tape cartridge 150 includes ahousing 152, a tape 122 in the housing 152, and a nonvolatile memory 156coupled to the housing 152. In some approaches, the nonvolatile memory156 may be embedded inside the housing 152, as shown in FIG. 1B. In moreapproaches, the nonvolatile memory 156 may be attached to the inside oroutside of the housing 152 without modification of the housing 152. Forexample, the nonvolatile memory may be embedded in a self-adhesive label154. In one preferred embodiment, the nonvolatile memory 156 may be aFlash memory device, ROM device, etc., embedded into or coupled to theinside or outside of the tape cartridge 150. The nonvolatile memory isaccessible by the tape drive and the tape operating software (the driversoftware), and/or other device.

By way of example, FIG. 2 illustrates a side view of a flat-lapped,bi-directional, two-module magnetic tape head 200 which may beimplemented in the context of the present invention. As shown, the headincludes a pair of bases 202, each equipped with a module 204, and fixedat a small angle α with respect to each other. The bases may be“U-beams” that are adhesively coupled together. Each module 204 includesa substrate 204A and a closure 204B with a thin film portion, commonlyreferred to as a “gap” in which the readers and/or writers 206 areformed. In use, a tape 208 is moved over the modules 204 along a media(tape) bearing surface 209 in the manner shown for reading and writingdata on the tape 208 using the readers and writers. The wrap angle θ ofthe tape 208 at edges going onto and exiting the flat media supportsurfaces 209 are usually between about 0.1 degree and about 5 degrees.

The substrates 204A are typically constructed of a wear resistantmaterial, such as a ceramic. The closures 204B made of the same orsimilar ceramic as the substrates 204A.

The readers and writers may be arranged in a piggyback or mergedconfiguration. An illustrative piggybacked configuration comprises a(magnetically inductive) writer transducer on top of (or below) a(magnetically shielded) reader transducer (e.g., a magnetoresistivereader, etc.), wherein the poles of the writer and the shields of thereader are generally separated. An illustrative merged configurationcomprises one reader shield in the same physical layer as one writerpole (hence, “merged”). The readers and writers may also be arranged inan interleaved configuration. Alternatively, each array of channels maybe readers or writers only. Any of these arrays may contain one or moreservo track readers for reading servo data on the medium.

FIG. 2A illustrates the tape bearing surface 209 of one of the modules204 taken from Line 2A of FIG. 2. A representative tape 208 is shown indashed lines. The module 204 is preferably long enough to be able tosupport the tape as the head steps between data bands.

In this example, the tape 208 includes 4 to 22 data bands, e.g., with 8data bands and 9 servo tracks 210, as shown in FIG. 2A on a one-halfinch wide tape 208. The data bands are defined between servo tracks 210.Each data band may include a number of data tracks, for example 1024data tracks (not shown). During read/write operations, the readersand/or writers 206 are positioned to specific track positions within oneof the data bands. Outer readers, sometimes called servo readers, readthe servo tracks 210. The servo signals are in turn used to keep thereaders and/or writers 206 aligned with a particular set of tracksduring the read/write operations.

FIG. 2B depicts a plurality of readers and/or writers 206 formed in agap 218 on the module 204 in Circle 2B of FIG. 2A. As shown, the arrayof readers and writers 206 includes, for example, 16 writers 214, 16readers 216 and two servo readers 212, though the number of elements mayvary. Illustrative embodiments include 8, 16, 32, 40, and 64 activereaders and/or writers 206 per array, and alternatively interleaveddesigns having odd numbers of reader or writers such as 17, 25, 33, etc.An illustrative embodiment includes 32 readers per array and/or 32writers per array, where the actual number of transducer elements couldbe greater, e.g., 33, 34, etc. This allows the tape to travel moreslowly, thereby reducing speed-induced tracking and mechanicaldifficulties and/or execute fewer “wraps” to fill or read the tape.While the readers and writers may be arranged in a piggybackconfiguration as shown in FIG. 2B, the readers 216 and writers 214 mayalso be arranged in an interleaved configuration. Alternatively, eacharray of readers and/or writers 206 may be readers or writers only, andthe arrays may contain one or more servo readers 212. As noted byconsidering FIGS. 2 and 2A-B together, each module 204 may include acomplementary set of readers and/or writers 206 for such things asbi-directional reading and writing, read-while-write capability,backward compatibility, etc.

FIG. 2C shows a partial tape bearing surface view of complimentarymodules of a magnetic tape head 200 according to one embodiment. In thisembodiment, each module has a plurality of read/write (R/W) pairs in apiggyback configuration formed on a common substrate 204A and anoptional electrically insulative layer 236. The writers, exemplified bythe write head 214 and the readers, exemplified by the read head 216,are aligned parallel to a direction of travel of a tape mediumthereacross to form an R/W pair, exemplified by the R/W pair 222.

Several R/W pairs 222 may be present, such as 8, 16, 32 pairs, etc. TheR/W pairs 222 as shown are linearly aligned in a direction generallyperpendicular to a direction of tape travel thereacross. However, thepairs may also be aligned diagonally, etc. Servo readers 212 arepositioned on the outside of the array of R/W pairs, the function ofwhich is well known.

Generally, the magnetic tape medium moves in either a forward or reversedirection as indicated by arrow 220. The magnetic tape medium and headassembly 200 operate in a transducing relationship in the mannerwell-known in the art. The piggybacked MR head assembly 200 includes twothin-film modules 224 and 226 of generally identical construction.

Modules 224 and 226 are joined together with a space present betweenclosures 204B thereof (partially shown) to form a single physical unitto provide read-while-write capability by activating the writer of theleading module and reader of the trailing module aligned with the writerof the leading module parallel to the direction of tape travel relativethereto. When a module 224, 226 of a piggyback head 200 is constructed,layers are formed in the gap 218 created above an electricallyconductive substrate 204A (partially shown), e.g., of AlTiC, ingenerally the following order for the R/W pairs 222: an insulating layer236, a first shield 232 typically of an iron alloy such as NiFe (−), CZTor Al—Fe—Si (Sendust), a sensor 234 for sensing a data track on amagnetic medium, a second shield 238 typically of a nickel-iron alloy(e.g., ˜80/20 at % NiFe, also known as permalloy), first and secondwriter pole tips 228, 230, and a coil (not shown). The sensor may be ofany known type, including those based on MR, GMR, AMR, tunnelingmagnetoresistance (TMR), etc.

The first and second writer poles 228, 230 may be fabricated from highmagnetic moment materials such as ˜45/55 NiFe. Note that these materialsare provided by way of example only, and other materials may be used.Additional layers such as insulation between the shields and/or poletips and an insulation layer surrounding the sensor may be present.Illustrative materials for the insulation include alumina and otheroxides, insulative polymers, etc.

The configuration of the tape head 126 according to one embodimentincludes multiple modules, preferably three or more. In awrite-read-write (W-R-W) head, outer modules for writing flank one ormore inner modules for reading. Referring to FIG. 3, depicting a W-R-Wconfiguration, the outer modules 252, 256 each include one or morearrays of writers 260. The inner module 254 of FIG. 3 includes one ormore arrays of readers 258 in a similar configuration. Variations of amulti-module head include a R-W-R head (FIG. 4), a R-R-W head, a W-W-Rhead, etc. In yet other variations, one or more of the modules may haveread/write pairs of transducers. Moreover, more than three modules maybe present. In further approaches, two outer modules may flank two ormore inner modules, e.g., in a W-R-R-W, a R-W-W-R arrangement, etc. Forsimplicity, a W-R-W head is used primarily herein to exemplifyembodiments of the present invention. One skilled in the art apprisedwith the teachings herein will appreciate how permutations of thepresent invention would apply to configurations other than a W-R-Wconfiguration.

FIG. 5 illustrates a magnetic head 126 according to one embodiment ofthe present invention that includes first, second and third modules 302,304, 306 each having a tape bearing surface 308, 310, 312 respectively,which may be flat, contoured, etc. Note that while the term “tapebearing surface” appears to imply that the surface facing the tape 315is in physical contact with the tape bearing surface, this is notnecessarily the case. Rather, only a portion of the tape may be incontact with the tape bearing surface, constantly or intermittently,with other portions of the tape riding (or “flying”) above the tapebearing surface on a layer of air, sometimes referred to as an “airbearing”. The first module 302 will be referred to as the “leading”module as it is the first module encountered by the tape in a threemodule design for tape moving in the indicated direction. The thirdmodule 306 will be referred to as the “trailing” module. The trailingmodule follows the middle module and is the last module seen by the tapein a three module design. The leading and trailing modules 302, 306 arereferred to collectively as outer modules. Also note that the outermodules 302, 306 will alternate as leading modules, depending on thedirection of travel of the tape 315.

In one embodiment, the tape bearing surfaces 308, 310, 312 of the first,second and third modules 302, 304, 306 lie on about parallel planes(which is meant to include parallel and nearly parallel planes, e.g.,between parallel and tangential as in FIG. 6), and the tape bearingsurface 310 of the second module 304 is above the tape bearing surfaces308, 312 of the first and third modules 302, 306. As described below,this has the effect of creating the desired wrap angle α₂ of the taperelative to the tape bearing surface 310 of the second module 304.

Where the tape bearing surfaces 308, 310, 312 lie along parallel ornearly parallel yet offset planes, intuitively, the tape should peel offof the tape bearing surface 308 of the leading module 302. However, thevacuum created by the skiving edge 318 of the leading module 302 hasbeen found by experimentation to be sufficient to keep the tape adheredto the tape bearing surface 308 of the leading module 302. The trailingedge 320 of the leading module 302 (the end from which the tape leavesthe leading module 302) is the approximate reference point which definesthe wrap angle α₂ over the tape bearing surface 310 of the second module304. The tape stays in close proximity to the tape bearing surface untilclose to the trailing edge 320 of the leading module 302. Accordingly,read and/or write elements 322 may be located near the trailing edges ofthe outer modules 302, 306. These embodiments are particularly adaptedfor write-read-write applications.

A benefit of this and other embodiments described herein is that,because the outer modules 302, 306 are fixed at a determined offset fromthe second module 304, the inner wrap angle α₂ is fixed when the modules302, 304, 306 are coupled together or are otherwise fixed into a head.The inner wrap angle α₂ is approximately tan⁻¹(δ/W) where δ is theheight difference between the planes of the tape bearing surfaces 308,310 and W is the width between the opposing ends of the tape bearingsurfaces 308, 310. An illustrative inner wrap angle α₂ is in a range ofabout 0.5° to about 1.1°, though can be any angle required by thedesign.

Beneficially, the inner wrap angle α₂ may be set slightly less on theside of the module 304 receiving the tape (leading edge) than the innerwrap angle α₃ on the trailing edge, as the tape 315 rides above thetrailing module 306. This difference is generally beneficial as asmaller α₃ tends to oppose what has heretofore been a steeper exitingeffective wrap angle.

Note that the tape bearing surfaces 308, 312 of the outer modules 302,306 are positioned to achieve a negative wrap angle at the trailing edge320 of the leading module 302. This is generally beneficial in helpingto reduce friction due to contact with the trailing edge 320, providedthat proper consideration is given to the location of the crowbar regionthat forms in the tape where it peels off the head. This negative wrapangle also reduces flutter and scrubbing damage to the elements on theleading module 302. Further, at the trailing module 306, the tape 315flies over the tape bearing surface 312 so there is virtually no wear onthe elements when tape is moving in this direction. Particularly, thetape 315 entrains air and so will not significantly ride on the tapebearing surface 312 of the third module 306 (some contact may occur).This is permissible, because the leading module 302 is writing while thetrailing module 306 is idle.

Writing and reading functions are performed by different modules at anygiven time. In one embodiment, the second module 304 includes aplurality of data and optional servo readers 331 and no writers. Thefirst and third modules 302, 306 include a plurality of writers 322 andno readers, with the exception that the outer modules 302, 306 mayinclude optional servo readers. The servo readers may be used toposition the head during reading and/or writing operations. The servoreader(s) on each module are typically located towards the end of thearray of readers or writers.

By having only readers or side by side writers and servo readers in thegap between the substrate and closure, the gap length can besubstantially reduced. Typical heads have piggybacked readers andwriters, where the writer is formed above each reader. A typical gap is25-35 microns. However, irregularities on the tape may tend to droopinto the gap and create gap erosion. Thus, the smaller the gap is thebetter. The smaller gap enabled herein exhibits fewer wear relatedproblems.

In some embodiments, the second module 304 has a closure, while thefirst and third modules 302, 306 do not have a closure. Where there isno closure, preferably a hard coating is added to the module. Onepreferred coating is diamond-like carbon (DLC).

In the embodiment shown in FIG. 5, the first, second, and third modules302, 304, 306 each have a closure 332, 334, 336, which extends the tapebearing surface of the associated module, thereby effectivelypositioning the read/write elements away from the edge of the tapebearing surface. The closure 332 on the second module 304 can be aceramic closure of a type typically found on tape heads. The closures334, 336 of the first and third modules 302, 306, however, may beshorter than the closure 332 of the second module 304 as measuredparallel to a direction of tape travel over the respective module. Thisenables positioning the modules closer together. One way to produceshorter closures 334, 336 is to lap the standard ceramic closures of thesecond module 304 an additional amount. Another way is to plate ordeposit thin film closures above the elements during thin filmprocessing. For example, a thin film closure of a hard material such asSendust or nickel-iron alloy (e.g., 45/55) can be formed on the module.

With reduced-thickness ceramic or thin film closures 334, 336 or noclosures on the outer modules 302, 306, the write-to-read gap spacingcan be reduced to less than about 1 mm, e.g., about 0.75 mm, or 50% lessthan standard LTO tape head spacing. The open space between the modules302, 304, 306 can still be set to approximately 0.5 to 0.6 mm, which insome embodiments is ideal for stabilizing tape motion over the secondmodule 304.

Depending on tape tension and stiffness, it may be desirable to anglethe tape bearing surfaces of the outer modules relative to the tapebearing surface of the second module. FIG. 6 illustrates an embodimentwhere the modules 302, 304, 306 are in a tangent or nearly tangent(angled) configuration. Particularly, the tape bearing surfaces of theouter modules 302, 306 are about parallel to the tape at the desiredwrap angle α₂ of the second module 304. In other words, the planes ofthe tape bearing surfaces 308, 312 of the outer modules 302, 306 areoriented at about the desired wrap angle α₂ of the tape 315 relative tothe second module 304. The tape will also pop off of the trailing module306 in this embodiment, thereby reducing wear on the elements in thetrailing module 306. These embodiments are particularly useful forwrite-read-write applications. Additional aspects of these embodimentsare similar to those given above.

Typically, the tape wrap angles may be set about midway between theembodiments shown in FIGS. 5 and 6.

FIG. 7 illustrates an embodiment where the modules 302, 304, 306 are inan overwrap configuration. Particularly, the tape bearing surfaces 308,312 of the outer modules 302, 306 are angled slightly more than the tape315 when set at the desired wrap angle α₂ relative to the second module304. In this embodiment, the tape does not pop off of the trailingmodule, allowing it to be used for writing or reading. Accordingly, theleading and middle modules can both perform reading and/or writingfunctions while the trailing module can read any just-written data.Thus, these embodiments are preferred for write-read-write,read-write-read, and write-write-read applications. In the latterembodiments, closures should be wider than the tape canopies forensuring read capability. The wider closures will force a widergap-to-gap separation. Therefore a preferred embodiment has awrite-read-write configuration, which may use shortened closures thatthus allow closer gap-to-gap separation.

Additional aspects of the embodiments shown in FIGS. 6 and 7 are similarto those given above.

A 32 channel version of a multi-module head 126 may use cables 350having leads on the same pitch as current 16 channel piggyback LTOmodules, or alternatively the connections on the module may beorgan-keyboarded for a 50% reduction in cable span. Over-under, writingpair unshielded cables can be used for the writers, which may haveintegrated servo readers.

The outer wrap angles at may be set in the drive, such as by guides ofany type known in the art, such as adjustable rollers, slides, etc. Forexample, rollers having an offset axis may be used to set the wrapangles. The offset axis creates an orbital arc of rotation, allowingprecise alignment of the wrap angle α₁.

To assemble any of the embodiments described above, conventional u-beamassembly can be used. Accordingly, the mass of the resultant head can bemaintained or even reduced relative to heads of previous generations. Inother approaches, the modules may be constructed as a unitary body.Those skilled in the art, armed with the present teachings, willappreciate that other known methods of manufacturing such heads may beadapted for use in constructing such heads.

As noted above, tape lateral expansion and contraction present manychallenges to increasing data track density on conventional products.Conventional products have attempted to compensate for tape lateralexpansion and contraction by controlling tape width by tension andimproving the characteristics of the media itself. However, thesemethods fail to fully cancel the tape lateral expansion and contraction,and actually lead to other problems, including tape stretch and mediacost increases, respectively.

FIGS. 8A-8C are intended to depict the effect of tape lateral expansionand contraction on transducer arrays position relative thereto, and arein no way intended to limit the invention. FIG. 8A depicts a module 800relative to the tape 802, where the tape has a nominal width. As shown,the transducers 804 are favorably aligned with the data tracks 806 onthe tape 802. However, FIG. 8B illustrates the effect of tape lateralcontraction. As shown, contraction of the tape causes the data tracks tocontract as well, and the outermost transducers 808 are positioned alongthe outer edges of the outer data tracks as a result. Moreover, FIG. 8Cdepicts the effect of tape lateral expansion. Here expansion of the tapecauses the data tracks to move farther apart, and the outermosttransducers 808 are positioned along the inner edges of the outer datatracks as a result. If the tape lateral contraction is greater than thatshown in FIG. 8B, or the tape lateral expansion is greater than thatshown in FIG. 8C, the outermost transducers 808 will cross onto adjacenttracks, thereby causing the adjacent tracks to be overwritten during awriting operation and/or resulting in readback of the wrong track duringa readback operation. Moreover, running effects, such as tape skew andlateral shifting may exacerbate such problems, particularly for tapehaving shingled data tracks.

Thus, it would be desirable to develop a tape drive system able to readand/or write tracks onto the tape in the proper position, regardless ofthe extent of tape lateral expansion and/or contraction at any giventime. Various embodiments described and/or suggested herein overcome theforegoing challenges of conventional products, by orienting at least twomodules of a tape drive system, such as by rotating, pivoting and/ortilting, thereby selectively altering the pitch of the transducers intheir arrays, as will soon become apparent.

By selectively orienting a module, the pitch of the transducers on themodule is thereby altered, preferably aligning the transducers with thetracks on a tape for a given tape lateral expansion and/or contraction.Tape contraction (shrinkage) can be dealt with by orienting a nominallynon-offset head, but tape expansion (dilation) cannot. Thus, toaccommodate both shrinkage and dilation about a “nominal,” the head mustbe statically positioned at a nominal angle of at least approximately0.2° as will be explained below. Thereafter, smaller angular adjustments(e.g., about 1° or lower, but could be more) may be made to thealready-oriented module in order to compensate for any variation of thetape lateral expansion and/or contraction, thereby keeping thetransducers aligned with tracks on the tape.

FIGS. 9A-9C illustrate representational views of the effects oforienting a module having transducer arrays. It should be noted that theangles of orientation illustrated in FIGS. 9A-9C are an exaggeration(e.g., larger than would typically be observed), and are in no wayintended to limit the invention.

Referring to FIG. 9A, the module 900 is shown relative to the tape 902,where the tape has a nominal width. As illustrated, the module 900 isoriented at an angle θ_(nom) such that the transducers 904 are favorablyaligned with the data tracks 906 on the tape 902. However, when the tape902 experiences tape lateral contraction and/or expansion, the datatracks 906 on the tape contract and/or expand as well. As a result, thetransducers on the module are no longer favorably aligned with the datatracks 906 on the tape 902.

In FIG. 9B, the tape 902 has experienced tape lateral contraction.Therefore, in a manner exemplified by FIG. 8B, the transducers 904 onthe module 900 of FIG. 9B would no longer be favorably aligned with thedata tracks 906 on the tape 902 if no adjustment were made. However, asalluded to above, smaller angular adjustments may be made to thealready-oriented module 900 in order to compensate for tape lateralcontraction. Therefore, referring again to FIG. 9B, the angle oforientation >θ_(nom) of the module 900 is further positioned at an anglegreater than θ_(nom). By increasing the angle >θ_(nom) the effectivewidth w₂ of the array of transducers decreases from the effective widthw₁ illustrated in FIG. 9A. This also translates to a reduction in theeffective pitch between the transducers, thereby realigning thetransducers along the contracted data tracks 906 on the tape 902 asshown in FIG. 9B.

On the other hand, when the tape experiences tape lateral expansion, thedata tracks on the tape expand as well. As a result, the transducers onthe module would no longer be favorably aligned with the data tracks onthe tape if no adjustments were made. With reference to FIG. 9C, thetape 902 has experienced tape lateral expansion. As a result, furtherangular adjustments may be made to the angle of orientation of themodule in order to compensate for the tape lateral expansion. Therefore,referring again to FIG. 9C, the angle of orientation <θ_(nom) of themodule 900 is reduced to an angle less than θ_(nom). By decreasing theangle of orientation <θ_(nom) the effective width w₃ of the array oftransducers 904 increases from the effective width w₁ illustrated inFIG. 9A. Moreover, reducing the effective width of the array oftransducers 904 also causes the effective pitch between the transducersto be reduced, thereby realigning the transducers along the data tracks906 on the tape 902.

In a preferred approach, magnetic tape systems have two or more modules,each having an array of transducers, typically in a row. Depending onthe desired embodiment, the additional rows of transducers may allow thesystem to read verify during the write process, but is not limitedthereto. As mentioned above, the foregoing conventional challenges maybe overcome, e.g., by rotating a given module about an axis orthogonalto the plane in which its array resides (e.g., parallel to the plane ofthe tape bearing surface), thereby selectively altering the pitch of thetransducers in the array.

By providing a system that compensates for tape lateral expansion and/orcontraction, various embodiments enable use of wider readers, resultingin a better signal to noise ratio (SNR), and/or smaller data tracks,resulting in a higher capacity per unit area of the media.

FIGS. 10A-10B depict an apparatus 1000 for compensating for tape lateralexpansion and/or contraction, in accordance with one embodiment. As anoption, the present system 1000 may be implemented in conjunction withfeatures from any other embodiment listed herein, such as thosedescribed with reference to the other FIGS. Of course, however, system1000 and others presented herein may be used in various applicationsand/or in permutations which may or may not be specifically described inthe illustrative embodiments listed herein. Further, the system 1000presented herein may be used in any desired environment.

Referring to FIGS. 10A-10B, the system 1000 includes modules 1002, 1004,each of which have an array 1006, 1008 of transducers 1010. The modules1002, 1004, are preferably fixed relative to each other. In view of thepresent description, “fixed” is intended to mean constrained from adirectional movement relative to each other such that the arrays of eachmaintain a fixed position relative to each other. According to variousapproaches, the modules may be fixed relative to each other by usingrods, fasteners, adhesives, cables, wire, etc. Moreover, according todifferent embodiments, the modules are preferably fixed relative to eachother prior to being installed in the system 1000, head, etc. dependingon the desired embodiment. However, the modules are preferablyselectively orientable (e.g., tiltable and/or rotatable) as a singlestructure about a pivot point while remaining fixed relative to eachother, as will soon become apparent.

With continued reference to FIGS. 10A-10B, the modules 1002, 1004, arepreferably fixed such that the axes 1012, 1013 of the arrays 1006, 1008are oriented about parallel to each other, respectively. As illustratedin FIGS. 10A-10B, the axes 1012, 1013 of each array of transducers aredefined by the dashed lines that lie between opposite ends thereof,e.g., positioned farthest apart.

Referring now to FIG. 10A, the array 1006 of a first module 1002 isoffset from the array 1008 of a second module 1004 in a first directionparallel to the axis 1013 of the array 1008 of the second module 1004.The modules 1002, 1004 are also set to a nominal angle in the drive sothat the transducers of the arrays are aligned along the data tracks 906on a tape 902 having nominal tape lateral expansion.

With continued reference to FIG. 10A, the arrays 1006, 1008 of thetransducers 1010 of the first and second modules are preferably offsetsuch that the transducers 1010 of the first module 1002 are aboutaligned with the transducers 1010 of the second module 1004 in adirection 1020 of tape travel thereacross when the axes are oriented atan angle φ between greater than about 0.05° and about 45°. Preferably,the angle φ is between greater than about 0.2° and about 10°, andideally between greater than about 0.25° and about 5°, relative to aline 1022 oriented perpendicular to the direction 1020 of tape travel.

In addition, the inventors have surprisingly and unexpectedly found thatthe various embodiments described below, and having the angle φ in therange between greater than about 0.2° and about 10°, enable writing andreading that does not steer the tape or cause media damage over the lifeof the tape. For example, the inventors expected the skiving edges ofthe modules to steer the tape laterally.

Angles of orientation greater than within the specified range (e.g.,greater than about 10°) are undesirable as the higher angles causesteering of the tape when used. However, as described above, the anglesof orientation within the specified range unexpectedly and unforeseeablydid not result in steering of the tape. Moreover, it is more difficultto distinguish between tape lateral expansion and/or contraction andskew when angles of orientation of the modules is greater than withinthe specified range. This may cause difficulties when matching thedimensional conditions of the tape and/or orientation of the modules ofthe current operation to that of the previous operation (explained infurther detail below). It should also be noted that the angle oforientation φ illustrated in FIG. 10A is exaggerated (e.g., larger thanwithin the desired range), and is in no way intended to limit theinvention.

Depending on the desired embodiment, the modules themselves may beoffset to effect the shifting of the transducer arrays, e.g., as shownby the offset (offset) in FIG. 10B. Alternatively, the transducer arraysmay be positioned on the respective module in a specified position toeffect the offset while the modules themselves are not offset in thedrive; or combinations thereof.

With continued reference to FIG. 10B, the system 1000 includes amechanism 1014, such as a tape dimensional instability compensationmechanism, for orienting the modules to control a transducer pitchpresented to a tape. The tape dimensional instability compensationmechanism 1014 preferably allows for the orienting of the modules to bedone while the modules are reading and/or writing. The tape dimensionalinstability compensation mechanism 1014 may be any known mechanismsuitable for orienting the modules. Illustrative tape dimensionalinstability compensation mechanisms 1014 include worm screws, voice coilactuators, thermal actuators, piezoelectric actuators, etc.

A controller 1016 in one approach is configured to control the tapedimensional instability compensation mechanism 1014 based on a readbacksignal of the tape, e.g., servo signals, data signals, a combination ofboth, etc. In another approach, the dimensional conditions of the tapeand/or orientation of the modules when the tape was written may beretrieved e.g., from a database, cartridge memory, etc., and theorientation may be set based thereon to about match the transducer pitchof the current operation to that of the previous operation.

In various approaches, additional logic, computer code, commands, etc.,or combinations thereof, may be used to control the tape dimensionalinstability compensation mechanism 1014 for adjusting the orientation ofthe modules based on a skew of the tape. Moreover, any of theembodiments described and/or suggested herein may be combined withvarious functional methods, depending on the desired embodiment.

FIG. 10C depicts a variation of an apparatus as shown in FIG. 10A, andlike elements are numbered the same in both FIGS. Referring to FIG. 10C,a spacer member 1050 extends between tape bearing surfaces of themodules. The spacer member 1050 may be recessed from a plane of the tapebearing surfaces, but is preferably coplanar therewith and/or otherwiseforms a portion of the overall tape bearing surface of the head.

In one approach, the spacer member 1050 includes a magnetic shield 1052for magnetically shielding the array of transducers from the secondarray of transducers. Such magnetic shield may be formed of any suitablematerial known in the art, such as NiFe, CoFe, etc. The magnetic shieldmay extend from the tape bearing surface, or some point therebelow, in aheight direction (into the tape bearing surface), preferably for adistance that provides the desired shielding effect. For example, theshield may have a height similar to that of shields of the transducers.

FIG. 10D depicts an alternate embodiment, similar to that of FIG. 10B,but having two sets of modules, where each set may include two or moremodules. Each set of modules is preferably independently orientable toset the angle of orientation. Each set may also be independentlypositionable for track following.

In one approach, the outer modules of each set may be configured forwriting, and the inner modules configured for reading. Thus, in oneillustrative use case, the writers on the outer module of one set maywrite while the readers of an inner module of the second set may readback the just-written track. In another illustrative use case, thewriters on the outer module of one set may write while the readers of aninner module of the same set may read back the just-written track.

FIG. 11 depicts a method 1100 for orienting modules having transducers,in accordance with one embodiment. Such method 1100 may be implementedby the controller of FIG. 10B. As an option, the present method 1100 maybe implemented in conjunction with features from any other embodimentlisted herein, such as those described with reference to the other FIGS.Of course, however, such method 1100 and others presented herein may beused in various applications and/or in permutations which may or may notbe specifically described in the illustrative embodiments listed herein.Further, the method 1100 presented herein may be used in any desiredenvironment.

Referring now to FIG. 11, the method 1100 includes determining a desiredpitch for transducers for reading and/or writing to a magnetic tape asillustrated in operation 1102. In one approach, the desired pitch may bedetermined by the state of the tape. An exemplary mechanism forestablishing the proper pitch is to use the timing interval read by twoservo readers to determine the state of the tape, e.g., contracted,expanded or nominal. Although a preferred mode is to use servo data,this is not absolutely required. Thus, it may be desirable to determinethe state of the tape, e.g., by incorporating any of the approachesdescribed and/or suggested herein and/or known processes, whendetermining the desired pitch. However, according to other approaches,the pitch may be determined using any approach described and/orsuggested herein, or combinations thereof.

Method 1100 further includes orienting a head to achieve the desiredpitch, the head having at least two opposing modules generally alignedwith each other in a(n intended) direction of tape travel thereacross,positions of the two modules being fixed relative to each other, eachmodule having an array of the transducers, where an axis of each arrayis defined between opposite ends thereof, where the array of a first ofthe modules is offset from the array of a second of the modules in afirst direction parallel to the axis of the array of the second modulesuch that the transducers of the first module are about aligned with thetransducers of the second module in a direction of tape travelthereacross when the axes are oriented at an angle between greater than0.2° and about 10° relative to a line oriented perpendicular to thedirection of tape travel. See operation 1104.

In another approach, steps 1102 and 1104 may be performed concurrently.For example, in one embodiment the proper transducer pitch may be basedon data signals. One way to implement this is by first setting thetransducer pitch at a nominal value by selecting a nominal angle, andthen adjusting the orientation thereof to obtain a better readbackquality across the read channels. The quality may be determined forexample by finding the lowest error rate, best signal to noise level,etc.

As an option, the system may continue or periodically monitor theappropriate signals and adjust the orientation. Adjustments can beperformed any time, such as during an initialization period prior toreading or writing user data, during readback or writing operations,etc.

Although two modules 1002, 1004 are illustrated in FIGS. 10A-10B, inother approaches, a system may include any number of modules e.g., atleast two, at least three, at least four, a plurality, etc. depending onthe desired embodiment. Referring to the illustrative embodimentdepicted in FIG. 12, which may be considered a modification of system1000 of FIG. 10A, the system 1200 shown may include a third module 1202positioned between the first and second modules 1002, 1004. As shown,the array of transducers of the third module 1202 is preferably offsetfrom the array of the first module 1002 in a first direction 1204.Moreover, the extent of the offset t₁ of the array of the third module1202 relative to the array of the first module 1002 is less than anextent of the offset t₂ of the array of the second module 1004 relativeto the array of the first module 1002.

According to different approaches, the first second and/or third modules1002, 1004, 1202 may be used for data writing and/or data reading,depending on the desired embodiment. Thus, the system 1200 may serve asa write-read-write (WRW) device if the first and second modules 1002,1004 are designed for at least data writing and the third module 1202 isdesigned for at least data reading. As an option, the first and secondmodules 1002, 1004 may be designed for data writing and not for datareading, and/or the third module 1202 maybe designed for data readingand not for data writing.

In another approach, the system 1200 may serve as a read-write-read(RWR) device if the first and second modules 1002, 1004 are designed forat least data reading and optionally not for data writing, while thethird module 1202 is designed for at least data writing and optionallynot for data reading. However, this is in no way meant to limit theinvention; according to various other approaches, a third, fourth,fifth, etc. module may be positioned with any orientation relative toother modules of the system, depending on the desired embodiment.

With continued reference to FIG. 12, according to one approach, theangle of orientation φ of the modules 1002, 1202, 1004 and distance ybetween the arrays may be used to calculate the offset x. Asillustrated, the offset x is between the arrays of transducers of themodules in a direction parallel to their axes 1012, 1206, which may becalculated using Equation 1.

tan(φ)=x/y  Equation 1

Equation 1 can be rewritten into Equation 2.

y(tan(φ))=x  Equation 2

Other known methods of calculating and/or assigning the offset x anddistance y between the arrays of any of the modules may be used in otherembodiments.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as “logic,” a “circuit,” “module,” or“system.” Furthermore, aspects of the present invention may take theform of a computer program product embodied in one or more computerreadable medium(s) having computer readable program code embodiedthereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a non-transitory computer readable storage medium. A computerreadable storage medium may be, for example, but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, or device, or any suitable combinationof the foregoing. More specific examples (a non-exhaustive list) of thenon-transitory computer readable storage medium include the following: aportable computer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a portable compact disc read-only memory (e.g.,CD-ROM), a Blu-ray disc read-only memory (BD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a non-transitory computerreadable storage medium may be any tangible medium that is capable ofcontaining, or storing a program or application for use by or inconnection with an instruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a non-transitory computer readable storage medium and that cancommunicate, propagate, or transport a program for use by or inconnection with an instruction execution system, apparatus, or device,such as an electrical connection having one or more wires, an opticalfibre, etc.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fibre cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer, for example through the Internet using an Internet ServiceProvider (ISP).

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart(s) and/orblock diagram block or blocks.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A computer program product for orienting a head,the computer program product comprising a computer readable storagemedium having program instructions embodied therewith, the programinstructions readable and/or executable by a controller to cause thecontroller to: determine, by the controller, a desired pitch fortransducers for reading and/or writing to a magnetic tape; and cause, bythe controller, a mechanism to orient a head to achieve the desiredpitch, the head having at least two opposing modules generally alignedwith each other in an intended direction of tape travel thereacross,positions of the two modules being fixed relative to each other, eachmodule having an array of the transducers, wherein an axis of each arrayis defined between opposite ends thereof, wherein the array of a firstof the modules is offset from the array of a second of the modules in afirst direction parallel to the axis of the array of the second modulesuch that the transducers of the first module are about aligned with thetransducers of the second module in the intended direction of tapetravel thereacross when the axes are oriented at an angle betweengreater than 0.2° and about 10° relative to a line orientedperpendicular to the intended direction of tape travel.
 2. The computerprogram product as recited in claim 1, comprising program instructionsreadable and/or executable by the controller to cause the controller todetermine a state of the tape, the desired pitch being determined basedon the state of the tape.
 3. A computer program product as recited inclaim 1, wherein the head has only two modules.
 4. A computer programproduct as recited in claim 1, wherein the head has three modules, athird one of the modules being positioned between the first and secondmodules, wherein the array of the third module is offset from the arrayof the first module in the first direction, wherein an extent of theoffset of array of the third module relative to the array of the firstmodule is less than an extent of the offset of the array of the secondmodule relative to the array of the first module.